Project Summary/Abstract: Allergy, asthma, and parasitic infections are characterized by a type 2 immune response, which is initiated and sustained in large part by the type 2 cytokines interleukin-4 (IL-4), IL-5, and IL-13. Type 2 innate lymphoid cells (ILC2s) are in fact the predominant source of IL-5 and IL-13 in early type 2 immune responses, and accordingly, ILC2s have been shown to be important contributors to the immune response in mouse models of atopic dermatitis, allergic lung inflammation, and helminth infection. In addition, recent studies have identified roles for type 2 cytokines and ILC2s in a wider range of biological contexts, including metabolic homeostasis and circadian immunity, but the details of how ILC2s originate and achieve their functions are poorly understood. Tissue-resident ILC2s appear shortly after birth, are long-lived, and can be further expanded by epithelial cytokines. However, whether the adult ILC2 population comprises persistent embryonic cells or whether the cells are being continually replenished is still unclear. Using a combination of lineage tracing (tamoxifen- inducible Cre mice) and labeling methods (doxycycline-regulated reporter mice and EdU labeling), we plan on determining the contribution of prenatal versus postnatal cells to the ILC2 populations in the neonatal and adult lungs (Aim 1). Furthermore, neonatal ILC2s localize to tissues shortly after birth and begin to produce IL-5, but the stimuli for ILC2s at this stage are unknown. Epithelial cytokines, e.g. IL-33, activate ILC2 populations residing at mucosal interfaces such as the lung and intestine, but the individual contributions of these cytokines to homeostatic ILC2 function in these tissues at steady state is still an active area of inquiry. Using two independent approaches (genetic knockout mice and inhibitory antibodies), we will test the requirement of these cytokines for ILC2 function during the neonatal period (Aim 2). In addition, we will assess whether modulation of the ILC2 pool during this neonatal period has long-term effects on host immunity (Aim 3). Investigating the cellular and molecular mechanisms by which the tissue ILC2 population arises and how tissue ILC2s are primed for their functions will lead to a better understanding of potential therapeutic targets for allergy and asthma, as well as other diseases influenced by a type 2 immune response.